The most common approach for providing hot water in both domestic and commercial settings involves the use of large tanks for the storage of hot water. Although such heated tank systems can provide hot water at a relatively high flow rate, they are inherently energy inefficient because the water in the tank is continually reheated even when water is not being used on a regular basis.
Another approach to providing hot water involves the use of a tankless water heater system that heats water only when hot water is being used. Such tankless water heater systems, also referred to as demand water heater systems, can often provide a more energy efficient means of heating water than storage systems using the same type of heating (e.g., gas, electric, etc.). However, one common draw back of traditional tankless water heater systems is the occurrence of temperature spikes upon changes in hot water demand. Traditional reservoir type hot water heaters typically do not experience temperature spikes with changes in hot water demand as hot water is provided from a water reservoir of substantially uniform temperature. In a traditional reservoir system, when hot water demand increases the system simply provides more hot water from the reservoir (until the hot water runs out). Should hot water demand suddenly decrease, the temperature of the hot water is not changed because it comes from a reservoir of constant temperature water.
In contrast, in a typical tankless hot water heater system, when hot water-demand increases the system must increase the energy output of its heating elements to respond to the increased demand (and concomitant increased input water flow rate). Temperature spikes in the output water can then occur when there is a sudden decrease in hot water demand because of the delay in adjusting the energy output of the heating elements for the reduction in input water flow rate. Such temperature spikes in the flow from water fixtures for human use (e.g., sinks, showers, etc.), besides being unpleasant, can cause a person to reflexively jerk their hand away from the water stream, which can pose risks to equipment or others if the person happens to be washing a fragile or sharp piece of equipment at the time.
Temperature spikes can be particularly troublesome for fixtures with automatic faucets (e.g., touch-free faucets) because of the very rapid shut-off characteristic (typically about 50 milliseconds) of the solenoid valves used in such faucets. However, automatic faucets are finding increasing use in commercial and public settings owing to their advantages in sanitation provided by their touch-free use (e.g., food-borne illness, infection, etc.) and water conservation.
There are many industrial, commercial and residential uses to which a tankless hot water system capable of delivering hot water with reduced temperature spikes could be applied. In addition to uses as more energy efficient residential, commercial and industrial hot water supplies for multiple water fixtures (e.g., multiple sinks, multiple showers), tankless hot water systems with reduced temperature spikes could be used to provide hot water for multiple portable, semi-portable or fixed decontamination showers, which in times of heavy use, for example, could be subject to repeated and rapid changes in hot water demand (e.g., showers being turned on and off repeatedly).
A need therefore continues to exist for hot water delivery systems that can provide hot water in a more energy efficient manner than storage tank systems yet without the objectionable temperature spikes upon sudden changes in hot water demand found in traditional electric tankless hot water heater systems.